How to Grow Onions: Growing Stages, Planting & Care Tips

Kasey Spencer
How to Grow Onions

I’ve learned a thing or two about growing various plants, vegetables, and herbs. Today, I’m excited to share my knowledge on how to grow onions — a staple in most kitchens and a versatile vegetable that adds a unique flavor to numerous dishes.

Growing onions is an excellent choice if you’re interested in home gardening or even an experienced green thumb looking to expand your vegetable garden. Not only are onions relatively easy to grow, but the satisfaction of cooking with homegrown onions is something every gardener should experience.

In this blog post, I’m going to guide you through the process of growing onions.

From understanding the anatomy of the onion to navigating the different growing stages, and providing care tips for a healthy yield — we’ll cover it all. By the end of this guide, you’ll have all the information you need to start your onion-growing journey. Let’s dive in!

Understanding Onions

Before we begin our onion-growing journey, let’s take a moment to understand these flavorful bulbs a little better.

Onions, scientifically known as Allium cepa, belong to the same family as garlic, shallots, leeks, and chives. They are biennials, typically grown as annuals, and are prized for their flavorful bulbs which form underground, and their green tops, often referred to as onion greens or scallions.

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There are several types of onions, each with its unique flavor profile, color, and size. The most common ones include:

1. Yellow Onions

Yellow onions
Image: Michael Martin // Wikimedia Commons

These are your all-purpose, go-to onions. They have a nice balance of astringency and sweetness in their flavor, becoming sweeter the longer they cook.

2. Red Onions

Common Misconceptions About Growing Onions
Image: Kasyap // Wikimedia Commons

With their deep purple outer skin and reddish flesh, these onions are fairly similar to yellow onions in flavor, though their layers are slightly less tender and meaty.

3. White Onions

These onions tend to have a sharper and more pungent flavor. They are also a bit sweeter than yellow onions.

4. Sweet Onions

As the name suggests, these onions have a higher sugar content than other varieties making them good for caramelizing. Their lower sulfur content also makes them milder and an excellent choice for raw use.

5. Green Onions or Scallions

These onions are harvested young, while their shoots are still green and fresh.

6. Shallots

These are smaller and more elongated than typical onions, with a milder flavor and a hint of garlic.

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Onions are cool-season crops, which means they grow best when temperatures are between 55 and 75 degrees Fahrenheit. They need a sunny location and well-draining soil to grow well. Understanding these basic principles about onions will help you provide the right care at the right time, ensuring a healthy and bountiful harvest.

Preparing for Planting Onions

Proper preparation is key to successfully growing onions. From selecting the right time to plant to preparing the soil, each step is crucial for your onions to thrive. Let’s dive into these steps in more detail:

1. Selecting the Right Time

Onions are typically planted in early spring, as soon as the ground can be worked in your area. They can tolerate frost and actually prefer cooler weather at the start of their growth.

2. Choosing the Right Location

Onions need at least 6 hours of sunlight a day, so choose a location in your garden that receives plenty of sun. If you’re planting in a pot or container, make sure it’s positioned in a sunny spot.

3. Preparing the Soil

Onions prefer well-drained, slightly acidic soil with a pH between 6.0 and 7.0. If your soil is heavy clay, consider amending it with compost or manure to improve its texture and drainage. Alternatively, you could grow your onions in raised beds or containers.

4. Preparing the Garden or Pot

Till the soil to a depth of about 12 inches to make it loose and workable. This step is especially crucial for onions because they form bulbs underground. Hard, compacted soil will hinder this bulb formation. If you’re planting in a container, make sure it’s at least 12 inches deep and has sufficient drainage holes.

5. Onion Sets, Transplants, or Seeds

You have three options when it comes to planting onions: onion sets (small, immature bulbs), transplants (young onion plants), and seeds. Onion sets and transplants offer a head start and are less susceptible to pests, making them the easiest for beginners. Seeds offer a wider variety in terms of types of onions but require more time and care.

This preparation might seem like a lot of work, but remember, a strong foundation is vital for your onions’ success. The time and effort you put in now will reward you with a bountiful harvest later on.

green onion planted at home
green onion planted at home

The Growing Stages of Onions

Growing onions is a fascinating process that spans several months and involves distinct stages. Recognizing these stages can help you provide the appropriate care at each point in the growth cycle.

1. Seed Germination

If you’ve planted onion seeds, the first stage is germination. This typically occurs 7–10 days after sowing, provided the soil temperature is between 50 and 85 degrees Fahrenheit. You’ll first notice tiny green shoots emerging from the soil. These shoots will grow rapidly in the first few weeks.

2. Seedling Stage

In the seedling stage, the green shoots will continue to grow, and tiny root systems will begin to establish. This is a crucial stage for establishing strong plants, so make sure your onions are well-watered and receive plenty of sunlight. If you’ve planted onion sets or transplants, their growth will begin with this stage.

3. Bulb Formation Stage

Around 30 days after planting (or when the plants have about 5 leaves each), the bulb formation stage begins. This is when the onion starts developing its bulb—the part we eat. The size of the bulb is generally proportionate to the size and number of the leaves. Each leaf corresponds to a layer in the bulb, so more leaves mean bigger, multi-layered bulbs.

4. Bulb Maturation Stage

This is the final growth stage when the bulbs continue to grow and mature. The leaves will begin to turn yellow and fall over—a sign that the plant is moving its energy from the leaves to the bulb.

5. Dormancy and Harvest

Once most of the leaves have fallen over, stop watering and leave the onions in the ground for a few more days to allow them to enter a dormant state. This makes them less likely to rot when stored. After this period, it’s time to harvest your onions!

Understanding these growth stages will help you provide the right care at the right time, significantly increasing your chances of a successful onion harvest.

How to Plant Onions

Armed with the right knowledge and preparation, it’s time to get your hands dirty and plant those onions. Here’s a step-by-step guide for each planting method:

1. Planting Onion Sets or Transplants

Create a furrow (a narrow trench) in the soil about 2 inches deep.

Place the onion sets or transplants into the furrow, root-side down, ensuring that they’re spaced about 4-6 inches apart. If you’re planting in rows, make sure each row is at least 1 foot apart to give the plants room to grow and bulb up.

Cover the sets or transplants with soil, leaving the tip of the onion just peeking out of the soil. Water them thoroughly.

2. Planting Onion Seeds

Sow the seeds directly into the soil at a depth of about 1/4 inch and cover them lightly with soil.

Keep the soil moist but not waterlogged. The seeds should germinate in 7-10 days.

Once the seedlings are a few inches tall and sturdy enough to handle, thin them out so that they’re spaced about 2-3 inches apart. This gives them enough room to bulb.

3. Post-Planting Care

Keep the soil consistently moist. Onions have shallow roots, so they’ll dry out quickly if not watered regularly.

Apply a layer of mulch around the plants to conserve moisture, suppress weeds, and regulate soil temperature.

Planting onions might seem daunting at first, but it’s actually a fairly straightforward process. With a bit of patience and the right care, you’ll soon see those tiny onion sets, transplants, or seeds grow into mature, flavorful bulbs.

onion growing stages

Onion Care Guide

The work doesn’t stop once your onions are in the ground. Onions require regular care to grow strong and healthy. Let’s look at what onion care involves:

1. Watering

Onions need a consistent supply of water, as they have a shallow root system. Aim for at least 1 inch of water per week, including rainfall. Water them a little more frequently in dry conditions, but avoid waterlogging the soil.

2. Fertilizing

Onions benefit from regular feeding. Use a nitrogen-rich fertilizer every few weeks until the bulbs start to form. At that point, stop fertilizing, as the plants should now focus their energy on bulb development.

3. Mulching

Mulching is not only great for conserving water and suppressing weeds, but it also helps to regulate soil temperature. Use organic mulch like compost, straw, or shredded leaves around your onion plants.

4. Pest and Disease Control

Onions can be prone to pests like thrips and diseases like onion blight. Regularly check your plants for signs of damage and take appropriate action. Using organic pesticides and fungicides can help protect your onions without harming beneficial insects or the environment.

5. Thinning

If you’ve started your onions from seeds, you’ll need to thin out the seedlings to ensure each plant has enough space to develop a bulb. Once the seedlings are a few inches tall, carefully remove extra plants so that the remaining onions are spaced about 2-3 inches apart.

6. Weeding

Keep the area around your onions free of weeds. Weeds compete with your onions for resources and can hinder their growth.

Onion care might seem like a lot of work, but most of these tasks take just a few minutes. Regular care can mean the difference between a meager harvest and a bumper crop.

Harvesting and Storing Onions

The moment you’ve been waiting for is finally here! Harvesting onions is rewarding and relatively straightforward. Here’s how to go about it:

1. Harvesting

Most onion varieties are ready to harvest when the bulbs are big and the tops have turned yellow and fallen over. This usually occurs 100 to 175 days after planting, depending on the variety.

To harvest, gently pull the onions out of the ground. If they resist, use a spade or garden fork to loosen the soil around them and then pull them out.

Once harvested, lay the onions on the soil surface or a clean, dry surface to dry out for a few days if the weather is dry and sunny. This process, known as curing, helps the outer layers of the onion to dry out and form protective skin.

2. Curing

If you can’t dry your onions outside because of the weather, move them to a warm, well-ventilated place indoors.

Turn the onions occasionally to ensure they dry evenly.

Proper curing can take up to two weeks, and the onions are ready when the outer skins are dry and crispy, and the necks (where the leaves were attached) are tight and dry.

3. Storing

Store your onions in a cool, dark, and well-ventilated place to prevent them from rotting or sprouting. A basement or cellar often works well.

Keep the onions in mesh bags or in a crate to allow for good airflow. Try to store them in a single layer, as piling onions on top of each other can promote rot.

Check your stored onions regularly and remove any that show signs of rotting to prevent the rot from spreading.

Wrapping it up

Growing your own onions can be an incredibly rewarding experience. From the initial planting to the final harvest, it’s a journey that involves patience, care, and a little bit of gardening know-how.

By following these steps, you’ll be well on your way to a successful onion harvest. Whether you’re using your homegrown onions in your cooking or sharing them with friends and family, you’ll be sure to enjoy the fruits of your labor. Happy gardening!

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